Superlative adjectives are used to describe the most extreme quality of something compared to a group. When using a superlative adjective like "the tallest" before a noun, "the" is generally used because it refers to a single item or group that possesses that quality. However, "the" is not used when there is a possessive such as "my best student." Additionally, "the" can be dropped later in the sentence after the superlative adjective is introduced, with no change in meaning.